Skill Forge Eval

Skill Evaluation Pipeline

Run structured evaluations against Claude Code skills to verify triggering, correctness, and quality using a multi-agent pipeline.

Process

Step 1: Define Eval Set

Accept eval definitions from:

• Path to eval set JSON: evals/evals.json or user-specified file
• Inline prompts: User provides eval queries directly
• Auto-generated: Generate from skill description (see Step 1b)

Eval set JSON schema:

{
  "skill_name": "my-skill",
  "skill_path": "./my-skill",
  "evals": [
    {
      "eval_id": 0,
      "eval_name": "descriptive-name",
      "prompt": "The user's task prompt",
      "input_files": [],
      "assertions": [
        {
          "name": "output-has-score",
          "check": "Output contains a numeric score between 0-100",
          "weight": 1.0
        }
      ],
      "should_trigger": true
    }
  ]
}

Step 1b: Auto-Generate Eval Set

If no eval set exists, generate one:

1. Read the skill's SKILL.md description and instructions
2. Run python scripts/generate_eval_set.py to produce a starter set
3. Present the generated set to the user for review and editing
4. User approves or modifies before proceeding

Step 2: Set Up Workspace

Create the eval workspace outside the skill directory to avoid confusing eval artifacts with skill files. Use a sibling directory or a dedicated location:

eval-workspace/
  iteration-1/
    eval-0/
      eval_metadata.json        # Assertions and config for this eval
      with_skill/
        outputs/                # Skill execution outputs
        timing.json             # Token count + duration
        grading.json            # Assertion results + evidence
      baseline/
        outputs/
        timing.json
        grading.json
    eval-1/
      eval_metadata.json
      with_skill/
        outputs/
        timing.json
        grading.json
      baseline/
        outputs/
        timing.json
        grading.json
    benchmark.json              # Aggregated metrics
    benchmark.md                # Human-readable report

For each eval directory, create eval_metadata.json from the eval set entry:

{
  "eval_id": 0,
  "eval_name": "descriptive-name",
  "prompt": "The user's task prompt",
  "assertions": [...],
  "should_trigger": true
}

Step 3: Execute Eval Runs

For each eval in the set, spawn two parallel runs:

With-skill run (delegate to agents/skill-forge-executor.md):

Execute this task:
- Skill path: 
- Task: 
- Input files: 
- Save outputs to: /iteration-/eval-/with_skill/outputs/
- Outputs to save: 

Baseline run (delegate to agents/skill-forge-executor.md):

• For new skills: run without the skill loaded
• For improved skills: run with the previous version (snapshot it first)

Save timing data to timing.json in each run directory:

{
  "total_tokens": 84852,
  "duration_ms": 23332,
  "total_duration_seconds": 23.3
}

Step 4: Grade Results

Delegate to agents/skill-forge-grader.md for each completed run:

1. Grade against assertions defined in eval_metadata.json
2. Save results to grading.json per run:

{
  "eval_id": 0,
  "run_type": "with_skill",
  "assertions": [
    {
      "name": "output-has-score",
      "passed": true,
      "evidence": "Found score: 87/100 on line 14"
    }
  ],
  "pass_rate": 1.0
}

Step 5: Aggregate and Analyze

1. Run python scripts/aggregate_benchmark.py /iteration- --skill-name
2. This produces benchmark.json and benchmark.md with:

• Pass rate per eval (with_skill vs baseline)
• Average time and token usage
• Improvement ratio (with_skill / baseline)

1. Delegate to agents/skill-forge-analyzer.md to:

• Surface patterns that aggregate stats might hide
• Identify consistently failing assertion types
• Flag regressions from previous iterations

Step 6: Present Results

Generate a summary report:

# Eval Report: [skill-name] — Iteration [N]

## Overall
| Metric | With Skill | Baseline | Delta |
|--------|-----------|----------|-------|
| Pass Rate | X% | Y% | +Z% |
| Avg Time | Xs | Ys | -Zs |
| Avg Tokens | X | Y | -Z |

## Per-Eval Results
| Eval | With Skill | Baseline | Status |
|------|-----------|----------|--------|
| eval-0 | PASS | FAIL | Improved |
| eval-1 | PASS | PASS | Maintained |

## Patterns & Insights
[From analyzer agent]

## Recommendations
[Specific improvements based on failures]

Step 7: Collect Feedback

Save user feedback to feedback.json:

{
  "reviews": [
    {
      "run_id": "eval-0-with_skill",
      "feedback": "the chart is missing axis labels",
      "timestamp": "2026-03-06T12:00:00Z"
    }
  ],
  "status": "complete"
}

Pass feedback to /skill-forge evolve for the next iteration.

Advanced: Blind Comparison

For rigorous A/B testing between skill versions:

1. Delegate to agents/skill-forge-comparator.md
2. Pass two directories: eval-/with_skill/outputs/ and eval-/baseline/outputs/
3. Comparator assigns random labels (Version A / Version B) so it cannot know which is new
4. Rates each output on assertion criteria from eval_metadata.json
5. Returns preference scores without knowing which is "new" vs "old"

Error Handling

• Executor timeout: If a run exceeds 5 minutes, terminate and mark as "timed_out": true in timing.json
• Executor failure: If a run crashes, save the error to error.txt in the run directory and continue with remaining evals
• Grading failure: If grading cannot determine pass/fail, mark assertion as "passed": null with evidence explaining why
• Missing files: If timing.json or grading.json is missing after a run, flag the eval as incomplete in the report
• Partial completion: Always aggregate and report whatever results are available — do not block on one failed eval

Quality Gates

Before marking an eval run as complete:

• [ ] All evals executed (with_skill + baseline)
• [ ] Timing data captured for every run
• [ ] All assertions graded with evidence
• [ ] Benchmark aggregated with pass rate, time, tokens
• [ ] Analyzer patterns documented
• [ ] Results presented to user

Source & license

This open-source skill is cataloged on AgentStack and links to its original source — we do not rehost the code.

• Author: AgriciDaniel
• Source: AgriciDaniel/skill-forge
• License: MIT
• Homepage: https://agricidaniel.com

Install and usage instructions live in the source repository linked above.